The air bag gas generating composition is required to have properties including (1) a suitable burning rate, (2) a low burning temperature, (3) capability of generating a large amount of gas, (4) low concentrations of toxic components in the generated gas and (5) a low shock ignitability. Further, there may arise a need for meeting stringent requirements that the air bag gas generating composition should retain the above-mentioned properties for a long term of at least 10 to 15 years even when, for example, a high temperature is maintained in an automobile in summer or at the tropics, desert area or the like for a long time or repeatedly. Whether an air bag gas generating composition can retain the required functions and can be stably used under such rigorous conditions for at least 10 to 15 years can be determined depending on whether the air bag gas generating composition can maintain the required properties after an accelerated heating test in which, for example, the composition is heated at 107.degree. C. for 400 hours.
The inventors of the present invention previously discovered that a metal complex of semicarbazide is superior in the performance characteristics of air bag gas generating agents. The inventors completed an invention based on this discovery and filed a patent application in Japan under No.347715/1996. They made further investigations, directing their attention to a manganese complex of semicarbazide among metal complexes of semicarbazide, and found the following in the course of investigations. When a manganese complex of semicarbazide, like other metal complexes, is prepared by bringing semicarbazide into contact with manganese nitrate in an air atmosphere, the obtained manganese complex of semicarbazide, unlike other metal complexes, is not heat-stable. After an accelerated heating test of heating at 107.degree. C. for 400 hours, the above complex shows weight loss of about 1.5 to about 5.2% or more and fails to maintain the required properties of air bag gas generating agents such as a suitable burning rate and low concentrations of toxic components in the generated gas.
Furthermore, an air bag gas generating composition is required to have a high rate of a combustion residue in an inflator.
A combustion residue is inevitably created by combustion of an air bag gas generating composition. Such combustion residue is separated by a filter disposed in an inflator from a gas generated by combustion of a gas generating composition. The inflator is designed to keep the combustion residue from leaking out of the inflator. If the combustion residue leaks out of the inflator, the air bag may be damaged, resulting in a likelihood of inflicting harm on the air bag user.
In recent years, there is a demand from automobile manufacturers for dimensional reduction of inflators compared with those heretofore used. To meet this demand, there is now a need for air bag gas generating compositions which have a property of showing a high rate of combustion residue in an inflator as the required properties of air bag gas generating compositions.
However, among the azide-based gas generating compositions and azide-free gas generating compositions heretofore proposed, those having this ability have not been developed.
For example, azide-based gas generating compositions, when burnt, give highly toxic sodium oxide (Na.sub.2 O) as a combustion residue. Therefore in this case, a filter should have a complicated structure for preventing the remainder from leaking out of the inflator. For this purpose, large-sized inflators are unavoidably used. Even if an inflator is designed to have a minimum size, currently its diameter is 100 mm at its smallest and can not be smaller than 100 mm.
On the other hand, azide-free gas generating compositions, for example, the metal complex of hydrazine and the metal complex of carbohydrazide disclosed in WO96/20147, are unsatisfactory in the rate of combustion residue in an inflator, failing to meet the above-mentioned need. In other words, when the metal complex of hydrazine and the metal complex of carbohydrazide disclosed in WO96/20147 are used, a structurally simplified filter can not be used for their low rate of combustion residue in an inflator, inevitably necessitating the use of a large-sized inflator. Currently the minimized diameter of a designed inflator is not smaller than 90 to 95 mm.
If we can develop an air bag gas generating composition assuring a high rate of combustion residue in an inflator, inflators could be made dimensionally smaller than those conventionally used. For example, inflators may be reduced in diameter to about 70 mm or less.